Investigation of nano structures on ta-C films made by gallium FIB lithography

Abstract

Focussed ion beam (FIB) writing is used as a direct lithography process on tetrahedral amorphous carbon (ta-C) layers with high sp3 content. Ion induced conversion of sp3 to sp2 bonded carbon atoms by means of 30keV Ga+ irradiation takes place and conducting sp2 rich sites were formed on the nano scale. Investigations of the conductivity of graphitic layers embedded in thin ta-C films were done concerning the influence of Ga+ fluence and substrate temperature. Van-der-Pauw (VDP) structures were produced by Ga+-FIB lithography partly in combination with optical lithography. Sheet resistance decreases with increasing Ga+ fluence and the lowest RS was achieved with 290Ω sq−1 at 1.6×1017cm−2 ion fluence. Conductivity of sp2 structures could be further improved by rapid thermal annealing (RTA) without degradation of the ta-C insulation. Graphitic nano wires (NWs) were fabricated by FIB writing which dimensions and conductivity were characterised. Width and height of the NWs increase with increasing Ga+ fluence in a width range of 50 to 150nm and height range of 3 to 23nm.